Final answer:
A compound fracture, or open fracture, is a broken bone that is visible through an opening in the skin and carries a high risk of infection.
Step-by-step explanation:
The term that indicates a broken bone that is visible through an opening in the skin is compound fracture (C).
A compound fracture, also known as an open fracture, occurs when the broken bone pierces the skin and carries a high risk of infection.
For example, in figure 6.20, (b) represents an open fracture, which is a type of compound fracture.